Communication system and communication method

ABSTRACT

Wireless communication wherein channel estimation accuracy is improved while keeping the position of each bit in a frame, even when a modulation system having a large modulation multiple value is used for a data symbol. An encoding operation encodes and outputs transmitting data (bit string) and a bit converting operation converts at least one bit of a plurality of bits constituting a data symbol to be used for channel estimation, among the encoded bit strings, into ‘1’ or ‘0’. A modulating operation modulates the bit string inputted from the bit converting operation by using a single modulation mapper and a plurality of data symbols are generated.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 16/376,047,filed Apr. 5, 2019, which was a continuation application of applicationSer. No. 16/155,234, filed Oct. 9, 2018, which was a continuation of15/901,290, filed Feb. 21, 2018, which was a continuation of 15/652,731filed Jul. 18, 2017, which was a continuation application of applicationSer. No. 15/363,595 filed Nov. 29, 2016, which was a continuationapplication of application Ser. No. 15/139,880 filed Apr. 27, 2016,which was a continuation application of 14/834,909 filed Aug. 25, 2015,which was a continuation application of application Ser. No. 14/603,845filed Jan. 23, 2015, which was a continuation application of applicationSer. No. 14/326,133 filed Jul. 8, 2014, which was a continuationapplication of application Ser. No. 14/071,301 filed Nov. 4, 2013, whichwas a continuation application of application Ser. No. 13/753,271 filedJan. 29, 2013, which was a continuation application of application Ser.No. 11/997,892 filed Feb. 4, 2008, which was a national stageapplication of PCT/JP2006/315521 filed Aug. 4, 2006, which was based onJapanese Application. No. 2005-228687 filed Aug. 5, 2005, the entirecontents of each of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus and aradio communication method.

BACKGROUND ART

In order to improve the accuracy of channel estimation in mobilecommunication, a conventional technique is proposed for carrying outtentative decision of data symbols, calculating a channel estimationvalue, weighting the channel estimation value according to thereliability of tentative decision data and combining two channelestimation values of the weighted channel estimation value and a channelestimation value calculated from the pilot symbol (refer to PatentDocument 1).

Upon channel estimation, this conventional technique uses a channelestimation value alone calculated from tentative decision data with thehigh reliability, and so improvement of the accuracy of channelestimation is anticipated.

Patent Document 1: Japanese Patent Application Laid-Open No.2000-82978

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, when a modulation scheme with a large M-ary modulation numbersuch as 16QAM is used for data symbols, the reliability of tentativedecision data decreases, and so, in the above conventional techniquewith a large M-ary modulation number such as 16QAM, improvement of theaccuracy of channel estimation is not anticipated.

In contrast with this, in order to suppress a transmission rate decreaseand improve the accuracy of channel estimation, a method may be adoptedof decreasing the M-ary modulation number for part of data symbols thanthe M-ary modulation numbers for other data symbols, realizing easytentative decision of part of the data symbols and thereby improving thereliability of tentative decision data.

However, this method can be adopted for modulation schemes with largeM-ary modulation numbers, but the number of bits forming part of datasymbols decreases due to the change in the M-ary modulation number andtherefore the position of each bit in the frame is sequentially shiftedforward from the data symbols for which the M-ary modulation number ischanged. Then, when the position of each bit is shifted, it is necessaryon the receiving side of the data symbols to carry out receptionprocessing supporting the shift and therefore reception processingbecomes complicated.

It is therefore an object of the present invention to provide a radiocommunication apparatus and radio communication method that, even when amodulation scheme with a large M-ary modulation number is used for adata symbol, can keep the position of each bit in the frame and improvethe accuracy of channel estimation.

Means for Solving the Problem

The radio communication apparatus according to the present inventionadopts a configuration including: a converting section that carries outbit conversion of at least one of a plurality of bits forming a firstdata symbol in a bit sequence, to 1 or 0; a modulating section thatmodulates the bit sequence after the bit conversion using a singlemodulation mapper to generate a plurality of data symbols including thefirst data symbol; and a transmitting section that transmits theplurality of data symbols.

Advantageous Effect of the Invention

According to the present invention, even when a modulation scheme with alarge M-ary modulation number is used for a data symbol, it is possibleto keep the position of each bit in the frame and improve the accuracyof channel estimation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of the radiocommunication apparatus on the transmitting side according to Embodiment1 of the present invention;

FIG. 2 is a block diagram showing a configuration of the radiocommunication apparatus on the receiving side according to Embodiment 1of the present invention;

FIG. 3 is a constellation diagram according to Embodiment 1 of thepresent invention (Example 1);

FIG. 4A is an example of bit conversion according to Embodiment 1 of thepresent invention (QPSK);

FIG. 4B is an example of bit conversion according to Embodiment 1 of thepresent invention (BPSK);

FIG. 4C is an example of bit conversion according to Embodiment 1 of thepresent invention (Pilot);

FIG. 5A is an example of a frame configuration according to Embodiment 1of the present invention (before bit conversion);

FIG. 5B is an example of a frame configuration according to Embodiment 1of the present invention (after bit conversion);

FIG. 6 is a constellation diagram according to Embodiment 1 of thepresent invention (Example 2);

FIG. 7A is an example of bit conversion according to Embodiment 1 of thepresent invention (8PSK);

FIG. 7B is an example of bit conversion according to Embodiment 1 of thepresent invention (QPSK);

FIG. 7C is an example of bit conversion according to Embodiment 1 of thepresent invention (BPSK);

FIG. 7D is an example of bit conversion according to Embodiment 1 of thepresent invention (Pilot);

FIG. 8 is an example of control information according to Embodiment 1 ofthe present invention (Example 1);

FIG. 9 is an example of control information according to Embodiment 1 ofthe present invention (Example 2);

FIG. 10A is an example of a frame configuration according to Embodiment2 of the present invention (before bit conversion);

FIG. 10B is an example of a frame configuration according to Embodiment2 of the present invention (after bit conversion);

FIG. 11 is an example of bit conversion according to Embodiment 3 of thepresent invention (after synthesis, BPSK);

FIG. 12 is a block diagram showing a configuration of the radiocommunication apparatus on the transmitting side according to Embodiment3 of the present invention;

FIG. 13 is a block diagram showing a configuration of the radiocommunication apparatus on the receiving side according to Embodiment 3of the present invention;

FIG. 14 is an example of a frame configuration according to Embodiment 3of the present invention (after bit conversion);

FIG. 15 is an example of bit conversion according to Embodiment 3 of thepresent invention (after synthesis, QPSK); and

FIG. 16 is an example of a frame configuration according to Embodiment 3of the present invention (after bit conversion).

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments or the present invention will be described withreference to the attached drawings.

EMBODIMENT 1

FIG. 1 shows a configuration of radio communication apparatus 100 on thetransmitting side according to this embodiment. Further, FIG. 2 shows aconfiguration of radio communication apparatus 200 on the receiving sideaccording to this embodiment. This radio communication apparatus 200receives data symbols transmitted from radio communication apparatus 100and carries out channel estimation.

In radio communication apparatus 100 shown in FIG. 1, coding section 101encodes transmission data (i.e. bit sequence) and outputs the result tobit conversion section 102.

Out of the encoded bit sequence, bit conversion section 102 converts atleast one of a plurality of bits forming the data symbols used inchannel estimation in radio communication apparatus 200, to “1” or “0, ”and outputs the bit to modulating section 103. Further, bit conversionsection 102 carries out bit conversion according to control informationinputted from control information extracting section 108. Bit conversionwill be described in detail later.

Modulating section 103 modulates the bit sequence inputted from bitconversion section 102 using a single modulation mapper, to generate aplurality of data symbols and outputs the data symbols to multiplexingsection 104.

Multiplexing section 104 multiplexes pilot symbols over the data symbolsand outputs the result to radio transmitting section 105. Here, thepilot symbols are time-multiplexed on a per frame basis.

Radio transmitting section 105 carries out transmitting processing suchas D/A conversion, amplification and up-conversion of the pilot symbolsand data symbols and transmits the result to radio communicationapparatus 200 shown in FIG. 2 from antenna 106.

Radio receiving section 107 receives a signal which is transmitted fromradio communication apparatus 200 and which includes control informationand data symbols, through antenna 106 and carries out receptionprocessing such as down-conversion and D/A conversion of this receivedsignal. The received signal after the reception processing is inputtedto control information extracting section 108.

Control information extracting section 108 extracts the controlinformation from the received signal and outputs the control informationto bit conversion section 102. Further, control information extractingsection 108 outputs the received signal after the control information isextracted, that is, the data symbol, to demodulating section 109.

Demodulating section 109 demodulates the data symbol into a bit sequenceand outputs the bit sequence to decoding section 110.

Decoding section 110 decodes the bit sequence to obtain received data.

On the other hand, in radio communication apparatus 200 shown in FIG. 2,radio receiving section 202 receives a signal which is transmitted fromradio communication apparatus 100 and which includes the pilot symbolsand data symbols, through antenna 201, and carries out receptionprocessing such as down-conversion and D/A conversion of the receivedsignal. The received signal after the reception processing is inputtedto pilot symbol extracting section 204 and conversion symbol extractingsection 205.

Pilot symbol extracting section 204 extracts the pilot symbol from thereceived signal and outputs the pilot symbol to channel estimatingsection 207. Further, pilot symbol extracting section 204 outputs thereceived signal after the pilot symbol is extracted, that is, the datasymbol, to demodulating section 203 and SINR detecting section 2092.

Conversion symbol extracting section 205 extracts the data symbolsubjected to bit conversion in radio communication apparatus 100, fromthe received signal, and outputs the result to tentative decisionsection 206.

Tentative decision section 206 carries out tentative decision of thedata symbol subjected to bit conversion in radio communication apparatus100 and outputs the data symbol after the tentative decision to channelestimating section 207.

Channel estimating section 207 calculates a channel estimation valueusing the pilot symbol. This channel estimation value is calculatedaccording to general channel estimation. Further, channel estimatingsection 207 calculates a channel estimation value using the data symbolafter the tentative decision by carrying out the same channel estimationas the pilot symbol. Both the channel estimation value calculated fromthe pilot symbol and the channel estimation value calculated from thedata symbol after the tentative decision are inputted to demodulatingsection 203 and channel variation detecting section 2091.

Demodulating section 203 corrects channel variation of the data symbolusing both the channel estimation value calculated from the pilot symboland the channel estimation value calculated from the data symbol afterthe tentative decision, demodulates a data symbol after the channelvariation is corrected to a bit sequence, and outputs the bit sequenceto decoding section 208.

Decoding section 208 decodes the hit sequence to obtain received data.

Channel variation detecting section 2091 detects the amount of channelvariation in the frame using both the channel estimation valuecalculated from the pilot symbol and the channel estimation valuecalculated from the data symbol after the tentative decision, andoutputs the result to conversion symbol determining section 2101.Further, when the amount channel variation is separately detected in thetime domain and the frequency domain, the amount of channel variation inthe time domain may be detected using the maximum Doppler frequency (fd)and the amount of channel variation in the frequency domain may bedetected using a delay profile.

SINR detecting section 2092 detects the SINR of each inputted datasymbol and outputs the detection result to conversion bit numberdetermining section 2102.

Channel variation detecting section 2091 and SINR detecting section 2092form detecting section 209.

Conversion symbol determining section 2101 determines a data symbolsubject to bit conversion at radio communication apparatus 100, based onthe amount of channel variation in the frame. When the amount of channelvariation is greater, conversion symbol determining section 2101increases the number of data symbols subject to bit conversion in theframe to further improve the accuracy of channel estimation. Byincreasing the number of data symbols subject to bit conversion, thenumber of data symbols with improved accuracy of tentative decisionincreases, so that it is possible to improve the accuracy of channelestimation. Further, conversion symbol determining section 2101 mayequally arrange data symbols subject to bit conversion in each frame andarrangement may be carried out such that the number of data symbolssubject to bit conversion increases gradually with distance from thepilot symbol. The determination result at conversion symbol determiningsection 2101 is inputted to control information generating section 211.

Conversion bit number determining section 2102 determines the number ofbits subject to conversion on a per data symbol basis, based on the SINRof each data symbol. Conversion bit number determining section 2102increases the number of bits subject to conversion for data symbols withpoorer SINR. When the number of bits subject to conversion is increased,the accuracy of tentative decision improves as described later, so thatit is possible to improve the accuracy of channel estimation. Thedetermination result at conversion bit number determining section 2102is inputted to control information generating section 211.

Further, conversion symbol determining section 2101 and conversion bitnumber determining section 2102 form determining section 210.

Control information generating section 211 generates the determinationresult at determining section 210, that is, control information showingthe data symbol subject to bit conversion and the number of bits subjectto conversion, and outputs the control information to multiplexingsection 212.

Coding section 213 encodes transmission data (i.e. bit sequence) andoutputs the encoded data to modulating section 214.

Modulating section 214 modulates the encoded bit sequence, to generate aplurality of data symbols and outputs the data symbols to multiplexingsection 212.

Multiplexing section 212 multiplexes the control information over thedata symbols and outputs the result to radio transmitting section 215.Here, control information is time-multiplexed on a per frame basis.

Radio transmitting section 215 carries out transmission processing suchas D/A conversion, amplification and up-conversion of the controlinformation and the data symbol and transmits the result to radiocommunication apparatus 100 shown in FIG. 1 from antenna 201.

Next, bit conversion will be described in detail.

As for the data symbol subject to bit conversion, that is, the datasymbol used for channel estimation in radio communication apparatus 200,bit conversion section 102 of radio communication apparatus 100 convertsat least one of a plurality of bits forming the data symbol, to “1” or“0,” as described below.

BIT CONVERSION EXAMPLE 1

FIG. 3 shows a constellation diagram for the modulation scheme of 16QAM.In this constellation diagram, signal points are arranged such that eachsymbol formed with bits b₁ to b₄ differs from adjacent symbols by onebit, to improve bit error rate performances. This signal pointconstellation is referred to as “Gray coding.”

Then, when a data symbol subject to bit conversion is one of signalpoint constellations shown in FIG. 3, bit conversion section 102forcibly converts the lower two bits, the lower three bits or all of thefour bits of bits b₁ to b₄ to “1.”

When the lower two bits are converted to “1,” the signal pointconstellation for the data symbol after bit conversion is one of “0011,”“0111,” “1111” and “1011,” as shown in FIG. 4A. In this case, in radiocommunication apparatus 200, similar to the constellation diagram forQPSK, tentative decision can be carried out by positive/negativedecision alone with respect to the I-axis and the Q-axis.

Further, when the lower three bits are converted to “1,” the signalpoint constellation for a data symbol after bit conversion is one of“0111” or “1111,” as shown in FIG. 4B. In this case, in radiocommunication apparatus 200, similar to the constellation diagram forBPSK, tentative decision can be carried out by positive/negativedecision alone with respect to the I-axis.

Furthermore, when all of the four bits are converted to “1,” the signalpoint constellation for the data symbol after bit conversion is “1111”alone as shown in FIG. 4C. In this case, in radio communicationapparatus 200, the data symbol can be regarded as the pilot symbol.

The accuracy of tentative decision in radio communication apparatus 200increases in the order of FIG. 4A (where the lower two bits areconverted to “1”), FIG. 4B (where the lower three bits are converted to“1”) and FIG. 4C (where all of the four bits are converted to “1”). Thenumber of bits subject to conversion is determined according to controlinformation transmitted from radio communication apparatus 200 asdescribed above.

Further, for example, in the frame configuration shown in FIG. 5A, Whenthe data symbol subject to bit conversion is determined data symbol S₄and the number of bits subject to conversion is determined three, thelower three bits (bits 14 to 16) of bits 13 to 16 forming data symbolS₄, are converted to “1.” As a result, in addition to channel estimationby means of pilot symbol PL, radio communication apparatus 200 can carryout channel estimation using symbol S₄ subjected to tentative decisionbased on the constellation diagram for BPSK, which is more accurate thanthe constellation diagram for 16QAM.

Furthermore, in any case of FIG. 4A to FIG. 4C, in a data symbol subjectto bit conversion, the number of bits before bit conversion and thenumber of bits after bit conversion are both four and do not change. Forexample, as shown in FIGS. 5A and 5B, the number of bits of data symbolS₄ subject to bit conversion is four even after bit conversion. As aresult, modulating section 103 of radio communication apparatus 100 cangenerate data symbol S₄ after bit conversion similar to other datasymbols by using 16QAM. That is, modulating section 103 can modulate abit sequence of bits 1 to 32 using a single modulation mapper for 16QAMeven after bit conversion.

Further, the number of bits subject to conversion is determinedaccording to the SINR, so that it is possible to minimize transmissionrate decrease.

BIT CONVERSION EXAMPLE 2

In bit conversion example 2, the constellation diagram shown in FIG. 6is used as the constellation diagram for 16 QAM. This constellationdiagram is a special constellation diagram where the signal pointconstellation for a data symbol after bit conversion is the signal pointconstellation for 8PSK. That is, in bit conversion example 2, bitconversion section 102 carries out bit conversion in accordance with thespecial constellation diagram where the signal point constellation for adata symbol after bit conversion is the signal point constellation for8PSK.

To be more specific, even when the data symbol subject to bit conversionis one of signal point constellations shown in FIG. 6, out of bits b₁ tob₄, the lowest one bit is forcibly converted to “0,” the lower two bitsto “1,” the lower three bits to “1,” or all of the four bits to “1.”

When the lowest one bit is converted to “0,” the signal pointconstellation for a data symbol after bit conversion is one of “0100,”“0110,” “0010,” “0000,” “1100,” “1110,” “1010,” and “1000,” as shown inFIG. 7A. In this case, radio transmission apparatus 200 can carry outtentative decision based on angle alone, similar to the constellationdiagram for 8PSK.

Further, when the lower two bits are converted to “1,” the signal pointconstellation for a data symbol after bit conversion is one of “01111,”“0011,” “1111 ,” and “1011,” as shown in FIG. 7B. In this case, in radiocommunication apparatus 200, similar to the constellation diagram forQPSK, tentative decision can be carried out by positive/negativedecision alone with respect to the I-axis and the Q-axis.

Further, when the lower three bits are converted to “1,” the signalpoint constellation for a data symbol after bit conversion is one of“0111” and “1111,” as shown in FIG. 7C. In this case, in radiocommunication apparatus 200, similar to the constellation on diagram forBPSK, tentative decision can be carried out by positive/negativedecision alone with respect to the I-axis alone.

Further, when all of the four bits are converted to “1,” the signalpoint constellation for a data symbol after bit conversion is “1111”alone, as shown in FIG. 7D. In this case, in radio communicationapparatus 200, a data symbol can be regarded as a pilot symbol.

The accuracy of tentative decision in radio communication apparatus 200increases in the order of FIG. 7A (where the lowest one bit is convertedto “0”), FIG. 7B (where the lower two bits are converted to “1”), FIG.7C (where the lower three bits are converted to “1”) and FIG. 7D (whereall of the four bits are converted to “1”). Furthermore, the number ofbits subject to conversion is determined according to controlinformation transmitted from radio communication apparatus 200 asdescribed above.

In this way, in bit conversion example 2, by using the specialconstellation diagram shown in FIG. 6, the signal point constellationfor a data symbol after bit conversion is the signal point constellationfor 8PSK. That is, it is possible to use more signal point constellationpatterns than in bit conversion example 1, as signal point constellationpatterns of data symbols after bit conversion. In this way, by using bitconversion example 2, it is possible to carry out more detailed controlaccording to the SINR than in bit conversion example 1, and furthersuppress transmission rate decrease.

Bit conversion examples 1 and 2 have been described.

Moreover, control information generated in control informationgenerating section 211 of radio communication apparatus 200 is shown inFIGS. 8 and 9. FIG. 8 shows that symbols subject to conversion aredetermined symbols 3, 5 and 7, and the numbers of conversion bits aredetermined 1, 3 and 2, respectively. Further, as described above, whenthe numbers of conversion bits are one, three and two, the signal pointconstellations correspond to 8 PSK, BPSK and QPSK, respectively.Therefore, as shown in FIG. 9, the modulation scheme may be included incontrol information instead of the number of conversion bits of FIG. 8.

In this way, according to this embodiment, when a modulation scheme witha large M-ary modulation number such as 16QAM is used for a data symbol,it is possible to keep the position of each bit in the frame and improvethe accuracy of channel estimation.

EMBODIMENT 2

In this embodiment, coding section 101 shown in FIG. 1 carries out errorcorrecting coding of transmission data (i.e. bit sequence) usingsystematic codes such as Turbo code and LDPC code. Coding section 101encodes the transmission bit sequence using systematic code and therebygenerates the systematic bits, which are transmission bits and are shownwith “S,” and parity bits, which are redundancy bits and are shown with“P.”

In this case, when error correcting coding is carried out usingsystematic codes, parity bits are less significant than systematic bits.That is, in radio communication apparatus 200, systematic bits aretransmission bits and, when systematic bits are lost, error rateperformances deteriorate, and, on the other hand, parity bits areredundancy bits, so that, even though some of parity bits are lost, itis possible to keep required error rate performances.

Then, bit conversion section 102 carries out the same bit conversion ofparity bits alone as in Embodiment 1.

For example, if in the frame configuration shown in FIG. 10A datasymbols subject to bit conversion are determined S₂, S₅ and S₇ and thenumbers of bits subject to conversion are three, three and two,respectively, as shown in FIG. 10B, parity bits of the lower three bitsof bits forming data symbol S₂ are converted to “1,” parity bits of thelower three bits of bits forming data symbol. S₅ are converted to “1”and parity bits of the lower two bits of bits forming data symbol S₇ areconverted to “1.”

In this way, according to this embodiment, by limiting bits subject tobit conversion in bit conversion section 102 to parity bits alone, it ispossible to prevent loss of systematic bits due to bit conversion and,consequently, suppress deterioration of error rate performances causedby bit conversion.

EMBODIMENT 3

In this embodiment, even when a data symbol is one of signal pointconstellation in FIG. 3, two middle bits b₂ and b₃ of bits b₁ to b₄ areinverted to be subjected to bit conversion and then subjected to vectorsynthesis with the data symbol before bit inversion.

For example, if data symbol “1011” in FIG. 3 is duplicated and the twomiddle bits are inverted, the data symbol after bit inversion will be“1101.” Then, if these data symbols are subjected to vector synthesis,the signal point constellation is signal point 11 shown in FIG. 11.Similarly, if data symbol “0101” in FIG. 3 is duplicated and the twomiddle bits are inverted, the data symbol after bit inversion will be“0011.” Then, when these data symbols are subjected to vector synthesis,the signal point constellation is signal point 12 of FIG. 11. In thisway, as for any data symbol shown in FIG. 3, the two middle bits in aduplicated data symbol are inverted and are vector-synthesized with thedata symbol before inversion (the data symbol of the duplicationsource), the signal point constellation for a synthesized symbol iseither one of signal point 11 or 12 alone of FIG. 11.

When the signal point constellation is either one of signal point 11 or12 shown in FIG. 11, in a radio communication apparatus on the receivingside, similar to the constellation diagram for BPSK, tentative decisioncan be carried out by positive/negative decision alone with respect tothe I-axis.

In this embodiment, radio communication apparatuses adopt the followingconfiguration.

FIG. 12 shows a configuration of radio communication apparatus 300 onthe transmitting side according to this embodiment. In FIG. 12, the sameconfigurations as in FIG. 1 (Embodiment 1) will be assigned the samereference numerals and overlapping description will be omitted. Further,FIG. 13 shows a configuration of radio communication apparatus 400 onthe receiving side according to this embodiment. In FIG. 13, the sameconfigurations as in FIG. 2 (Embodiment 1) are assigned the samereference numerals and overlapping description will be omitted.

In radio communication apparatus 300 shown in FIG. 12, bit conversionsection 301 duplicates bits 9 to 12 forming data symbol 83 in an encodedbit sequence as shown in, for example, FIG. 14, and acquires data symbolS_(4.) Then, bit conversion section 301 carries out bit conversion byinverting the two middle bits (bits 10 and 11) of bits 9 to 12 formingdata symbol S₄ and outputs the result to modulating section 103.

On the other hand, in radio communication apparatus 400 shown FIG. 13,conversion symbol extracting section 401 extracts data symbol S₄subjected to bit conversion in radio communication apparatus 300, fromthe received signal and outputs the result to synthesizing section 403.Further, adjacent symbol extracting section 402 extracts previous,adjacent data symbol (that is, data symbols of the duplication source)S₃ to data symbol S₄ subject to bit conversion in radio communicationapparatus 300 and outputs the result to synthesizing section 403.

Synthesizing section 403 carries out vector synthesis of data symbol S₃and data symbol S₄ and outputs the synthesized symbol generated by thevector synthesis, to tentative decision section 404.

Tentative decision section 404 carries out tentative decision of thesynthesized symbol and outputs the synthesized symbol after tentativedecision to channel estimating section 207.

Further, even when a data symbol is any one of signal pointconstellation shown in FIG. 3, all of bits b₁ to b₄ are inverted to besubjected to bit conversion and are vector-synthesized with the datasymbol before bit inversion, the signal point constellation for thesynthesized symbol becomes one of four signal points for QPSK. When thesignal point constellation is one of four signal points for QPSK, inradio communication apparatus 400, similar to the constellation diagramfor QPSK, tentative decision can be carried out by positive/negativedecision alone with respect to the I-axis and Q-axis.

For example, when data symbol “1011” in FIG. 3 is duplicated and all ofthe four bits are inverted, the data symbol after bit inversion is“0100.” Then, when these data symbols are vector-synthesized, the signalpoint constellation is signal point 24 of FIG. 15. Similarly, when datasymbol “0101” in FIG. 3 is duplicated and all of the four bits areinverted, the data symbol after bit conversion is “1010.” Then, whenthese data symbols are vector-synthesized the signal point constellationis signal point 23 of FIG. 15. In this way, as for any data symbol shownin FIG. 3, by inverting all of the four bits of duplicated data symbolsand vector-synthesizing the data symbols with the data symbol (the datasymbol of the duplication source) before inversion, the signal pointconstellation for the synthesized symbol is one of signal points 21 to24 alone in FIG. 15.

When all of the four bits are inverted, bit conversion section 301duplicates bits 9 to 12 forming data symbol S₃ in the encoded bitsequence shown in, for example, FIG. 16, and acquires data symbol S₄.Then, bit conversion section 301 carries out bit conversion of all ofthe four bits 9 to 12 forming data symbol S₄ by inverting the bits andoutputs the result to modulating section 103.

In this way, in this embodiment, similar to Embodiment 1, the accuracyof tentative decision in radio communication apparatus 400 increases inthe order of inversion of ail of bits b₁ to b₄ and inversion of the twomiddle bits of bits b₁ to b₄. Then, in this embodiment, the number ofbits subject to conversion is determined according to controlinformation transmitted from radio communication apparatus 400, similarto Embodiment 1.

In this way, according to this embodiment, similar to Embodiment 1, evenwhen a modulation scheme with a large M-ary modulation number such as16QAM is used for data symbols, it is possible to keep the position ofeach bit in the frame and improve the accuracy of channel estimation.

Further, by using the previous, adjacent data symbol to the data symbolsubjected to bit conversion, as a data symbol of the duplication source,it is possible to minimize channel variations between both data symbolsand, consequently, minimize decision errors with the synthesized symbol.

The embodiments of the present invention have been described.

Although, in FIG. 5A, FIG. 5B, FIG. 10A, FIG. 10B and FIG. 14, one frameis formed with one pilot symbol (i.e. PL) and eight data symbols (S₁ toS₈) for ease of explanation, the frame configuration which enables thepresent invention is not limited to this configuration.

Further, radio communication apparatus 100 or 300 is provided in a radiocommunication base station apparatus (hereinafter simply “base station”)in a mobile communication system and radio communication apparatus 200or 400 is provided in a radio communication mobile station apparatus(hereinafter simply “mobile station”) in a mobile communication system,so that, even when a modulation scheme with a large M-ary modulationnumber such as 16QAM is used with respect to a data symbol transmittedin downlink, it is possible to keep the position of each bit in theframe and improve the accuracy of channel estimation in the mobilestation. Further, by providing radio communication apparatus 100 or 300in a mobile station and radio communication apparatus 200 or 400 in abase station, even when a modulation scheme with a large M-arymodulation number such as 16QAM is used with respect to a data symboltransmitted in uplink, it is possible to keep the position of each bitin the frame and improve the accuracy of channel estimation in the basestation.

Furthermore, in the above embodiments, the base station and mobilestation may be referred to as Node B and UE, respectively.

Furthermore, although cases have been described with the aboveembodiments where the number of conversion bits are determined based onthe SINR, the number of conversion bits may be determined based on theSNR, SIR, CINR, received power, interference power, bit error rate,throughput or the MCS (i.e. Modulation and coding Scheme) which achievespredetermined error rate, instead of the SINR. That is, in the presentinvention, the number of conversion bits is determined based on one ofthe above parameters showing received quality.

Also, although cases have been described with the above embodiment asexamples where the present invention is configured by hardware. However,the present invention can also be realized by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC”, “system LSI”, “super LSI”, or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The present application is based on Japanese Patent Application No.2005-228687, filed on Aug. 5, 2005, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a mobile communication systemand the like.

1. A communication system comprising a transmitting apparatus and a receiving apparatus, wherein the transmitting apparatus comprising: a receiver, which, in operation, receives, from the receiving apparatus, control information associated with a number of bits; circuitry, which, in operation: generates a bit sequence by forcibly setting each place of the number of bits determined from the control information out of a plurality of bits to a 1, the plurality of bits forming a modulation symbol in the bit sequence; and modulates the bit sequence by mapping the plurality of bits on a single modulation mapper, the single modulation mapper having first signal points; and a transmitter, which, in operation, transmits, to the receiving apparatus, the bit sequence, and the receiving apparatus comprising: a transmitter, which, in operation, transmits, to the transmitting apparatus, the control information; and a receiver, which, in operation, receives, from the transmitting apparatus, the bit sequence, wherein said circuity, in operation, forcibly sets each place of the number of bits to the 1 in a way that the plurality of bits are mapped to one of second signal points, which are a part of the first signal points, a distance between the second signal points being equivalent to a largest of distance existing among the first signal points in an I-Qplane of the single modulation mapper.
 2. The communication system according to claim 1, wherein the single modulation mapper has 16 first signal points for 16 QAM, and the second signal points are a constellation of BPSK, QPSK or 8-PSK which is included in the single modulation mapper.
 3. The communication system according to claim 1, wherein the control information is associated with two as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower two bits of the plurality of bits to the
 1. 4. The communication system according to claim 1, wherein the control information is associated with three as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower three bits of the plurality of bits to the
 1. 5. The communication system according to claim 1, wherein the control information is associated with four as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower four bits of the plurality of bits to the
 1. 6. A communication system comprising a transmitting apparatus and a receiving apparatus, wherein the transmitting apparatus comprising: a receiver, which, in operation, receives, from the receiving apparatus, control information associated with a number of bits; circuitry, which, in operation: generates a bit sequence by forcibly setting each place of the number of bits determined from the control information out of a plurality of bits to a 1, the plurality of bits forming a modulation symbol in the bit sequence; and modulates the hilt sequence by mapping the plurality of bits on a single modulation mapper, the single modulation mapper having first signal points; and a transmitter, which, in operation, transmits, to the receiving apparatus, the bit sequence, and the receiving apparatus comprising: a transmitter, which, in operation, transmits, to the transmitting apparatus, the control information; and a receiver, which, in operation, receives, from the transmitting apparatus, the bit sequence, wherein said circuitry, in operation, forcibly sets each place of the number of bits to the 1 in a way that the plurality of bits are mapped to one or second signal points, which are a part of the first signal points, such that said modulation symbol is detected by positive or negative decision only with respect to at least one of an I-axis and a Q-axis in the single modulation mapper.
 7. The communication system according to claim 6, wherein the single modulation mapper has 16 first signal points for 16 QAM, and the second signal points are a constellation of BPSK, QPSK or 8-PSK which is included in the single modulation mapper.
 8. The communication system according to claim 6, wherein the control information is associated with two as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower two bits of the plurality of bits to the
 1. 9. The communication system according to claim 6, wherein the control information is associated with three as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower three bits of the plurality of bits to the
 1. 10. The communication system according to claim 6, wherein the control information is associated with four as the number of bits, and said circuitry, in operation, generates the bit sequence by forcibly setting each place of the lower four bits of the plurality of bits to the
 1. 11. A communication method comprising: transmitting, from a receiving apparatus to a transmitting apparatus, the control information; receiving, at the transmitting apparatus, the control information; generating, at the transmitting apparatus, a bit sequence by forcibly setting each place of the number of bits determined from the control information out of a plurality of bits to a 1, the plurality of bits forming a modulation symbol in the at sequence; modulating, at the transmitting apparatus, the bit sequence by mapping the plurality of bits on a single modulation mapper, the single modulation mapper having first signal points; transmitting, from the transmitting apparatus to the receiving apparatus, the bit sequence; and receiving, at the receiving apparatus, the bit sequence, wherein each place of the number of bits is forcibly set to the 1 in a way that the plurality of bits are mapped to one of second signal points, which are a part of the first signal points, a distance between the second signal points being equivalent to a largest of distances existing among the first signal points in an I-Q plane of the single modulation mapper.
 12. The communication method according to claim 11, wherein the single modulation mapper has 16 first signal points for 16 QAM, and the second signal points area constellation of BPSK, QPSK or 8-PSK which is included in the single modulation mapper.
 13. The communication method according to claim 11, wherein the control information is associated with two as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower two bits of the plurality of bits to the
 1. 14. The communication method according to claim 11, wherein the control information is associated with three as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower three bits of the plurality of bits to the
 1. 15. The communication method according to claim 11, wherein the control information is associated with four as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower four bits of the plurality of bits to the
 1. 16. A communication method comprising: transmitting, from a receiving apparatus to a transmitting apparatus, the control information; receiving, at the transmitting apparatus, the control information; generating, at the transmitting apparatus, a bit sequence by forcibly setting each place of the number of bits determined from the control information out of a plurality of bits to a 1, the plurality of bits forming a modulation symbol in the bit sequence; modulating, at the transmitting apparatus, the bit sequence by mapping the plurality of bits on a single modulation mapper, the single modulation mapper having first signal points; transmitting, from the transmitting apparatus to the receiving apparatus, the bit sequence; and receiving, at the receiving apparatus, the bit sequence, wherein each place of the number of bits is forcibly set to the 1 in a way that the plurality of bits are mapped to one of second signal points, which are a part of the first signal points, such that said modulation symbol is detected by positive or negative decision only with respect to at least one of an I-axis and a Q-axis in the single modulation mapper.
 17. The communication method according to claim 16, wherein the single modulation mapper has 16 first signal points for 16 QAM, and the second signal points area constellation of BPSK, QPSK or 8-PSK which is included in the single modulation mapper.
 18. The communication method according to claim 16, wherein the control information is associated with two as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower two bits of the plurality of bits to the
 1. 19. The communication method according to claim 16, wherein the control information is associated with three as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower three bits of the plurality of bits to the
 1. 20. The communication method according to claim 16, wherein the control information is associated with four as the number of bits, and the bit sequence is generated by forcibly setting each place of the lower four bits of the plurality of bits to the
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